A barrage of Katyusha rockets targeted an Iraqi air base that houses American troops south of the city of Mosul on Friday, two security officials said. The rocket fire appears to have originated in Mosul and struck the Iraqi army base in Qayyara, about 60 kilometers (38 miles) south of Mosul, where a U.S.-led coalition is helping Iraqi forces battle remnants of the Islamic State group. Iraq announced victory over IS two years ago, but the extremist group is still active through sleeper cells and frequently mount attacks on Iraqi security forces.